Identification and protection of security documents

ABSTRACT

The present invention provides methods and systems that are helpful for authenticating or protecting physical and electronic documents like financial documents and identification documents. One claim recites a method including: receiving digital data corresponding to a physical document; transforming the digital data into a frequency domain; comparing characteristics associated with the transformed digital data to predetermined characteristics that are associated with a first document type, and if the characteristics coincide, determining that the physical document is of the first document type; and if the characteristics do not coincide, comparing the characteristics of the transformed digital data to predetermined characteristics that are associated with a second document type, and if the characteristics coincide, determining that the physical document is of the second document type. Of course, other claims and combinations are provided as well.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.11/312,247, filed Dec. 19, 2005 (now U.S. Pat. No. 7,239,734) which is adivisional of U.S. patent application Ser. No. 10/170,223, filed Jun.10, 2002 (now U.S. Pat. No. 6,978,036). The 10/170,223 application is acontinuation in part of U.S. patent application Ser. No. 09/939,298,filed Aug. 24, 2001 (now U.S. Pat. No. 6,804,379), which is acontinuation of Ser. No. 09/127,502, filed Jul. 31, 1998 (now U.S. Pat.No. 6,345,104). Each of the above-mentioned patent documents is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention provides methods and features for authenticatingidentification documents and banknotes.

BACKGROUND AND SUMMARY OF THE INVENTION

In parent application Ser. No. 09/127,502 (U.S. Pat. No. 6,345,104) wedisclose the following: Many security documents are still designedlargely by hand. A designer works at a drafting table or computerworkstation, and spends many hours laying-out minute (e.g. 5 mm×5 mm)excerpts of the design. To aid integration of watermark and/orcalibration pattern data in this process, an accessory layout grid canbe provided, identifying the watermark “bias” (e.g. −3 to +3) that is tobe included in each 250 micron cell of the security document. If theaccessory grid indicates that the luminance should be slightly increasedin a cell (e.g. 1%), the designer can take this bias in mind whendefining the composition of the cell and include a touch less ink thanmight otherwise be included. Similarly, if the accessory grid indicatesthat the luminance should be somewhat strongly increased in a cell (e.g.5%), the designer can again bear this in mind and try to include moreink than might otherwise be included. Due to the substantial redundancyof most watermark encoding techniques, strict compliance by the designerto these guidelines is not required. Even loose compliance can result inartwork that requires little, if any, further modification to reliablyconvey watermark and/or calibration information.

Such “designing-in” of embedded information in security documents isfacilitated by the number of arbitrary design choices made by securitydocument designers. A few examples from U.S. banknotes include the curlsin the presidents' hair, the drape of clothing, the clouds in the skies,the shrubbery in the landscaping, the bricks in the pyramid, the fillpatterns in the lettering, and the great number of arbitrary guillochepatterns and other fanciful designs, etc. All include curves, folds,wrinkles, shadow effects, etc., about which the designer has widediscretion in selecting local luminance, etc. Instead of making suchchoices arbitrarily, the designer can make these choices deliberately soas to serve an informational—as well as an aesthetic—function.

To further aid the security document designer, data defining severaldifferent information-carrying patterns (both watermark and/orcalibration pattern) can be stored on mass storage of a computerworkstation and serve as a library of design elements for futuredesigns. The same user-interface techniques that are employed to pickcolors in image-editing software (e.g. Adobe Photoshop) and filltextures in presentation programs (e.g. Microsoft PowerPoint) cansimilarly be used to present a palette of information patterns to asecurity document designer. Clicking on a visual representation of thedesired pattern makes the pattern available for inclusion in a securitydocument being designed (e.g. filling a desired area).

In the embodiment earlier-described, the calibration pattern is printedas a visible artistic element of the security document. However, thesame calibration effect can be provided subliminally if desired. Thatis, instead of generating artwork mimicking the gray-scale pattern ofthe reference calibration block, the reference calibration block canitself be encoded into the security document as small changes in localluminance. In many such embodiments, the bias to localized documentluminance due to the calibration pattern is simply added to the bias dueto the watermark data, and encoded like the watermark data (e.g. aslocalized changes to the width or position of component line-art lines,as inserted ink droplets, etc.).

The present invention continues and improves these inventive ideas.According to one aspect of the present invention, an identificationdocument includes a security enhancer (e.g., perhaps hidden in line art,artwork or graphic designs). The security enhancer includes a groupingof concentric circles. The concentric circles share a common center, andeach circle is equally spaced from one another by a spacing distance d.Personal information carried by the identification document (e.g.,driver's license number, birth date, photograph, biometric information,name or address, etc., etc.) is reduced by a hash algorithm. The resultof the hash algorithm is a number. The number forms the spacing distanced for the grouping of concentric circles—personalizing the securityenhancer to the cardholder. The identification document is printed toinclude the customized security enhancer.

The repetitive spacing distance d of the plurality of concentric circlesin a spatial domain has an identifiable frequency response in afrequency domain. In particular, the corresponding frequency domainresponse includes a circle with a radius that is indirectly related tothe spacing distance d. The frequency domain response (or frequencydomain radius) can be evaluated to determine a counterfeit or forgery.

Banknotes, security documents, deeds, legal instruments, etc. can besimilarly marked.

Other aspect of the invention utilizes a security enhancer for documentidentification or classification. A security enhancer's frequencycharacteristics are compared against expected characteristics toidentify or classify the document.

Additional features and advantages of the present invention will becomemore apparent with reference to the following detailed description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an identification document including a security enhancer.

FIG. 2 is an enlarged view of the FIG. 1 security enhancer.

FIG. 3 is a graphical representation of a frequency domain response ofthe FIG. 2 security enhancer.

FIGS. 4 a and 4 b respectively illustrate a technique for providing asecurity enhancer, and a technique for verifying the authenticity of adocument including a security enhancer.

FIGS. 5 a and 5 b illustrate parallel line-based security enhancers.

FIGS. 6 a and 6 b illustrate frequency responses for the FIGS. 5 a and 5b security enhancers, respectively.

FIG. 7 illustrates a noisy frequency domain space corresponding to asecurity enhancer including concentric circles.

FIGS. 8 and 9 graphically illustrate the frequency space shown in FIG. 8in terms of circle radius and peak magnitude.

DETAILED DESCRIPTION

The presently preferred embodiments are described with respect to anidentification (ID) document. An identification document may include,e.g., a passport, identification paper, driver's license, identificationcard, company identification badge, secure area or network access badgeor card, etc., etc. We note, however, that the present invention is notso limited. Indeed, our inventive techniques can be similarly applied tobank notes, security documents, legal instruments, visas, productpackaging and labels, advertisements, badges, papers and printed matter,etc., etc.

With reference to FIG. 1, an ID document 10 may include a “card-shaped”substrate 21, historically made from a material such as paper orplastic, and even synthetics such as Teslin®. (Teslin® is available fromPPG Industries, One PPG Place, Pittsburgh, Pa. 15272 U.S.A). ID document10 will typically include a photograph 14 and various data 12, e.g.,such as textual information, graphics, a screened-back or hidden image,bar codes, biometric information (e.g., a fingerprint), personalinformation (e.g., name, address, birth date, ID number, etc.), or thelike. Of course both sides of substrate 21 can receive printing.

The printed substrate 21 is usually laminated. The laminate typicallyincludes a polyester or polycarbonate-based top sheet 23 and bottomsheet 25 that respectively overlay the top and bottom of the substrate21. Heat and/or adhesives and pressure are used to bond the laminatesheets 23 and 25 with the substrate 21. Or a laminate can include apouch into which the substrate 21 slips. Again, heat and/or adhesivesand pressure are used to bond the substrate 21 with a pouch laminate.The laminates provide a protective covering for the printed substrateand provide a level of protection against unauthorized tampering. (Forexample, a laminate would have to be removed to alter the printedinformation and then subsequently replaced after the alteration.). Alaminate layer 23 or 25 may optionally carry information like a cardbearer's signature or security features.

In some implementations, information may also be optically ormagnetically stored on recording media (e.g., magnetic stripe 27)carried by the laminate 25. Of course the magnetic stripe 27 can bealternatively carried by substrate 21 or laminate 23.

We note that the present invention encompasses ID documents includingmore or less features and layers than are illustrated in FIG. 1.

ID document 10 includes a security enhancer 16. The security enhancer 16can be printed (or laser engraved) on the substrate 21 or a laminate 23or 25. Security enhancer 16 provides an indicator to help determine theauthenticity of ID document 10. In one implementation, the indicatorprovides a frequency domain indication. In another implementation, theindicator provides a spatial domain indication. And in yet anotherimplementation, the indicator provides both a frequency domainindication and a spatial domain indication.

With reference to FIGS. 1 and 2 the illustrated security enhancer 16includes a grouping of concentric circles 1, 2, 3 and 4. (We note thatthe illustrated security enhancer 16 has been exaggerated to simplifythis disclosure. Security enhancer 16 will typically be incorporated ina background pattern, line art, graphic or artwork design. Securityenhancer 16 will oftentimes be relatively smaller than photograph 14 anddata 12. In other case, the security enhancer will be relatively larger,e.g., when placed in a background pattern.). The circles are evenlyspaced with respect to one another. For example, the distance betweenthe edge of circle 1 and the edge of circle 2 is d; the distance betweenthe edge of circle 2 and the edge of circle 3 is d; and a distancebetween the edge of circle 3 and the edge of circle 4 is also d. Thisconsistent spacing yields an identifiable frequency when examined in thefrequency domain (e.g., Fourier domain). The FIG. 2 security enhancer'sfrequency response includes a circular pattern 30 as shown in FIG. 3.

The circle spacing distance d (FIG. 2) and the frequency domain,circular radius r (FIG. 3) are inversely related. The relationship canbe expressed as:d=k·TRS/r,  Equation 1where k is a constant, and TRS is a transform sampling size factor(e.g., Fast Fourier transform sample size, discrete cosine transformsample size, relative sample size, etc.). The transform sampling sizefactor TRS helps compensate for differences in sample size (e.g., 64points vs. 128 points, etc.), if needed. We note that in many situationsTRS will be replaced by 1, e.g., when a base sampling size is employed.The distance r may be measured from the DC frequency component (locatedat the graphical origin in FIG. 3) to the circle 30. We note that theconstant k is preferably 1 when scanning an image at a resolution equalto the original printing resolution, e.g., scanning a 100 dpi image at100 dpi. The constant k can be adjusted to compensate for differences inscanning resolution and printing resolution. For example, when scanninga 100 dpi printed image at 300 dpi the frequency domain response shrinksby ⅓. The constant can be set to 3 to offset the shrinking. Or whenscanning a 100 dpi printed image at 50 dpi, the frequency response isdoubled. The constant can be set to ½ to compensate.

We use the circle spacing d and/or the circular radius r to provideincreased security for ID document 10. With reference to FIG. 4 a, weselect a set of information from the photograph 14 and/or data 12 (step40). The selected set of information is preferably unique to thecardholder or otherwise represents personal information. For example, wemay select the date of birth as the set of information. Or we select thebiometric fingerprint, photograph, photograph subset, or name andaddress, etc. We reduce the selected set of information to obtain anumber (step 42). For example, we reduce the selected set of informationwith a hashing algorithm. (Most generally, a hashing algorithm convertsthe set of information into a lower number of bits or directly to anumber. For example, an ASCII text string may be converted into a numberor lower number of bits. Or a photograph or biometric fingerprint may besimilarly reduced to produce a number. Conventional hashing algorithmsinclude MD4, MD5 or SHS-1, etc.).

The result of the hashing algorithm preferably produces a number. (Orthe output of the hashing algorithm is used to generate a number.). Thisnumber is used to set or adjust the spacing distance d (FIG. 2) for thesecurity enhancer 16 (step 44). In another implementation, the number isused to offset a predetermined spacing distance to achieve apersonalized spacing distance d. The security enhancer 16 is printed orapplied to the document 10 after the distance d is adjusted (step 46).Hence, personalized ID document information (e.g., photograph, birthdate and/or name, etc.) is used to customize the security enhancer 16 bysetting a spacing distance d.

An authentication method for a document including a security enhancer isdiscussed with reference to FIG. 4 b. An image of ID document 10 isscanned or otherwise captured (step 41). For example a digital camera,PC web camera or scanner captures an image of ID document 10. The cameracommunicates the captured image to a computer or processing circuitrythat is executing software instructions. The software instructionstransform the captured image into a frequency domain, e.g., a FourierTransform Domain (step 43). The equal spacing of the concentric circlesin the spatial domain produces a frequency response in the frequencydomain, namely, the response is a circle having a radius r. The radius ris determined or measured, e.g., in the frequency domain or from alogarithmic transform of the frequency domain (step 45).

The radius r is compared to an expected value r or range of values r(step 47). In one implementation, we select the same set of informationthat was used to originally seed the hash algorithm for setting thecircle spacing distance d in ID document 10. The hash algorithm hashesthe selected set of information to produce a number d. The number d andthe determined radius r are compared via Equation 1, with the constant kand TRS being adjusted, if needed, to account for printing and imagecapture dpi and sample size. If d and k·TRS/r coincide the ID documentis considered authentic (step 48). Otherwise the document is considereduntrustworthy (step 49).

In another implementation, we calculate d with the hash algorithm, andthen calculate an expected radius r value with Equation 1. We comparethe expected r value with the measured or determined r value. If theexpected r value and the measured r value are equal (or fall within anacceptable tolerance range) the ID document 10 is considered authentic.Otherwise the ID document 10 is considered untrustworthy.

In still another implementation, after obtaining the measured ordetermined radius r, we calculate a value d with Equation 1. Wedetermine an expected value for d using the corresponding hashingalgorithm. If the expected d value and the calculated d value are equal(or fall within an acceptable tolerance range) the ID document 10 isconsidered authentic. Otherwise the ID document 10 is considereduntrustworthy.

In some implementations our security enhancer includes both a spatialcomponent (e.g., the circle spacing d) and a frequency component (e.g.,the frequency circle radius r). The authenticity of a document can beverified by a relationship between the spatial component and thefrequency component.

In other implementations we verify authenticity of a document byexamining only one of these components. For example, we focus on thespatial domain component. We use pattern recognition and/or line or edgedetection techniques to identify the spacing distance d. An image of IDdocument 10 is captured. The captured image is analyzed with pattern orline detection techniques (software) to discern the pattern associatedwith the security enhancer. Edge or line detectors, e.g., Hough and/orRadon transforms or generalized versions of such, are employed todiscern a spacing distance d between elements of the security feature.The discerned spacing distance d is compared with an expected spacingdistance d to determine whether the ID document is authentic.

In another implementation, we focus on the frequency domain component.The frequency response may correspond to a graphic or artwork elementthat is inherently used in the subject document. We use the frequencyresponse of the security enhancer to identify a type of document. If afrequency response is found to have a first radius (orshape/location/characteristic), or otherwise falls within apredetermined range of radii, the corresponding document is determinedto be an ID document. Or if the frequency response is found to have asecond radius (or shape/location/characteristic), or otherwise fallswithin a predetermined range of radii, the corresponding document isdetermined to be a banknote, etc. Once a document is identified, a copydeterrent system can decide whether to allow printing of the document.For example, if a document is determined, based on its frequencycharacteristics, to be a bank note or identification document, the copydeterrent system stymies a copy operation.

Our authentication methods are helpful in preventing forgers. Forexample, suppose an identification document includes a securityenhancer. The identification document belongs to say 16-year old Joan.The identification card further includes Joan's photograph and printedinformation evidencing Joan's personal information (e.g., name, sex, ageand address, etc.). Joan decides that she wants to “up-grade” her age,by cutting and pasting her identification card photograph onto her22-year old sister, Molly's, identification card. Molly's identificationcard also includes a security enhancer and Molly's personal information(e.g., name, sex, age and address, etc.).

Joan pulls off a professional job replacing Molly's photograph with herown. All seems fine for Joan until an authentication process is used toverify the identification document. A hash of Joan's photograph is usedas an expected value d for the spacing distance of the securityenhancer. The expected d value, however, does not match the actual valued, since the actual value d was determined from a hash of Molly'sphotograph, and not Joan's. (Or a frequency domain characteristiccorresponding to Molly's security enhancer, like a radius r, is measuredand compared with a calculated value or to a calculated spacing distanced.). The counterfeit is justly determined.

In an alternative embodiment, ID document 10 includes a digitalwatermark. Digital watermarking is a process for modifying physical orelectronic media to embed a machine-readable code into the media. Themedia may be modified such that the embedded code is imperceptible ornearly imperceptible to the user, yet may be detected through anautomated detection process.

Digital watermarking systems typically have two primary components: anencoder that embeds the digital watermark in a host media signal, and adecoder that detects and reads the embedded digital watermark from asignal suspected of containing a digital watermark (a suspect signal).The encoder embeds a digital watermark by altering the host mediasignal. The reading component analyzes a suspect signal to detectwhether a digital watermark is present. In applications where thedigital watermark encodes information, the reader extracts thisinformation from the detected digital watermark.

Several particular digital watermarking techniques have been developed.The reader is presumed to be familiar with the literature in this field.Particular techniques for embedding and detecting imperceptiblewatermarks in media signals are detailed in the assignee's co-pendingU.S. patent application Ser. No. 09/503,881 (now U.S. Pat. No.6,614,914) and U.S. Pat.No. 6,122,403, which are each hereinincorporated by reference.

Returning to the alternative embodiment, a digital watermark embedded inID document 10 carries a payload or plural-bit data (e.g., a key). Thekey reveals which set of information is used to seed the hash algorithm.The key can include the set of information itself (e.g., by carrying thebirth date or document number) or can include a numeric indicator (e.g.,101 implies the birth date, while 110 implies the document number,etc.). Still further, the key may include a database pointer which canbe used to point to a database record. The database record reveals whichset of information was used to seed the hash algorithm. In a relatedimplementation, instead of using a digital watermark to carry suchinformation, the document itself may provide the clues. For example, thethird number of an ID document number may signal which set ofinformation was used to seed the hash algorithm. Or barcode informationand/or a magnetic stripe can provide the key. In a relatedimplementation, we encrypt the digital watermark payload, barcode ordata carried by the magnetic stripe to provide additional security.

To verify authenticity in this alternative embodiment, the digitalwatermark (or other indicator) is decoded to retrieve the key. The keyidentifies the set of information. The set of information is collectedand used to seed the hash algorithm. The hash algorithm produces anumber, which if the document is authentic, should correspond to thespacing distance d and/or to the frequency domain radius r.

Up to this point in the disclosure we have focused on a securityenhancer 16 that includes a grouping of concentric circles. We note thatthe present invention is not so limited. Indeed, the present inventionencompasses other security enhancers having characteristics that yieldidentifiable spatial domain and frequency responses. For example,consider the security enhancers illustrated with respect to FIGS. 5 aand 5 b. In FIG. 5 a the security enhancer includes a plurality ofparallel lines. The parallel lines are spaced equally at a distance d′.The frequency of spacing between the parallel lines in the spatialdomain results in a peak or magnitude point in the frequency domain.With reference to FIG. 6 a, a frequency point is location at a distancer′ from the DC component. (Of course we recognize that a transform,e.g., the Fourier transform, will include symmetric points correspondingto the peak. Accordingly, we have illustrated two frequency points inFIG. 6 a.). The distance r′ is related to the spacing distance d′ by thefollowing equation:d′=k·TRS/r′,  Equation 2where k is a constant and TRS is a transform sampling size factor asdiscussed above with respect to Equation 1.

Another alternative security enhancer is shown in FIG. 5 b. In thespatial domain, the security feature includes a plurality of parallellines, spaced apart from one another by a distance d″, and positioned atan angle θ with respect to an XY axis (dashed lines) as shown. In thefrequency domain, with reference to FIG. 6 a, the security enhancerincludes a point that is offset from the horizontal axis by the angle θat a distance r″. The relationship between d″ and r″ is expressed as:d″=k·TRS/r″,  Equation 3where k is a constant, TRS is a transform sampling size factor, asdiscussed above with respect to Equation 1, and r_(x)″=cos θ, andr_(y)″=sin θ.

We note that other security designs (such as parallel—butsquiggly—lines, spaced evenly apart, concentric half-circles, evenlyspaced arcs, parallel lines formed by concentric triangle, squares,octagons, etc., etc.) will yield identifiable frequency responses. Theseother security designs can be suitable interchanged with the presentinvention, particularly if the design characteristics can be adjusted toaccommodate personal information or predetermined security features. Wenote that while these other designs may be used as security enhancers,they may have a plurality of frequency responses which may need to besorted to identify the authenticating frequency clue.

A library of security enhancers can be made available to a designer orID document issuer. The library may include graphics or digitalrepresentations of the group of concentric circles, squiggly lines,parallel lines, etc. In the case of an ID document, after capturing aphotograph or personal information related to the cardholder, a hashalgorithm reduces a set of captured photograph or personal informationto a spacing distance d. The library (or a cooperating software module)uses the spacing d to adjust a selected security enhancer. The selectedsecurity enhancer is thus personalized to the cardholder. (We note thatin the case of an ID document issuer, like a state DMV, the selection ofa security enhancer will typically be standardized. Hence, each IDdocument may include the same basic security enhancer, but each securityenhancer will be personalized via the individualized spacing distance.).

One alternative frequency-circle radius calculation (or determination)technique converts a Cartesian circle representation (e.g., FIG. 3) intoa polar coordinate representation. A horizontal component of collectedpeak values is determined and used as the radius value, or used todetermine the radius value.

Detection in Noisy Environments

Now consider the frequency domain (i.e., Fourier Domain) space shown inFIG. 7. The circular frequency response 70 corresponds to a grouping ofconcentric circles in the spatial domain. The frequency space is noisy.The FIG. 7 frequency space includes many other frequency characteristics72 (e.g., corresponding to a design including semi-circles) andfrequency points 74. In such a noisy environment, frequency magnitudescan be measured (or graphically collected) as in FIG. 8. Applying a logpolar transform to FIG. 7, and then averaging along an axis θ, producedthe FIG. 8 graph. The circle 70 radius length corresponds to the spikeor peak between the 834 and 883 radius markers. If the radius peak isnoisy, as is the case with the peak between the 834 and 883 radiusmarkers, we can detect the radius by comparing a suspected peak to thelocal average of its neighboring values. For example, we can take anaverage of the peaks between 834 and 883, excluding the suspected peakitself, and then compare the suspected peak to the average. In thisexample implementation, if the local peak average is m, and the standarddeviation of the local peaks values is σ, then the thresholds, T1 andT2, can be used to narrow in on the circle's 70 actual radius. Letssuppose that T1=m−α·σ, and T2=m+α·σ, where α is constant determined,e.g., empirically for a given security enhancer. Then, if T1<suspectedpeak value<T2, the suspected peak value is ignored, otherwise thesuspected peak value is recorded. FIG. 9 shows the result of the aboveprocess when applied to the data represented by FIG. 8. The peak justbeyond the 847 marker comprises the circle 70's radius r.

Alternative Applications

An alternative application of our present invention is a copy detectionmechanism. We can minimize the circle spacing d (e.g., FIG. 2) of asecurity enhancer such that copying (e.g., scanning and printing) willblur or blend adjacent circle edges. The copy will appear more like onecircle instead of a group of concentric circles. Hence, while theoriginal security enhancer will include a frequency response having acircle r, a copy will not. The copy is confirmed when the expectedfrequency response is not determined.

Another inventive alternative application uniquely assigns a spacingdistance d per user or printer location. The security enhancerautomatically defaults to a particular spacing depending on who ishandling a document. Say for example, that John has a copy of aclassified document. John prints the document. Prior to printing, asecurity application (perhaps a plug-in or operating system module)applies a security enhancer to the print. The security enhancer includesa spacing that is uniquely assigned to John. Then, if the printeddocument is found in an unexpected channel, the spacing can be analyzedto determine who printed, and therefore leaked, the document. Thesecurity enhancer can be similarly modified to reflect a certain printeror intended receiver of the document.

CONCLUSION

The foregoing are just exemplary implementations of the presentinvention. It will be recognized that there are a great number ofvariations on these basic themes. The foregoing illustrates but a fewapplications of the detailed technology. There are many others.

For example, the security feature illustrated in FIGS. 1, 2, 5 a and 5 bcan include more or less circles or lines. Of course, the strength ofthe frequency response will increase as the number of circles or linesincreases. We also note that while the present invention has beendescribed by seeding a hash algorithm with personal information to set asecurity enhancer spacing distance d, the hash algorithm output couldalternatively be used to set the expected value of the frequency domainresponse r, which can be mathematically manipulated to achieve a spatialdomain spacing distance d. Moreover, while we have outlined specificrelationships between d and r, the present invention is intended toencompass other relationships between a security enhancer's spatial andfrequency domain characteristics. These relationships can be used withour security enhancer.

We note that our inventive techniques can be expanded to video. A videoframe may include a security enhancer (e.g., subliminally placed, or asbackground). The spacing may be set by reference to a video distributor,target recipient, or studio, etc. The security feature may also beapplied to rough cuts as a marking tool and to prevent unauthorizeddistribution. The security enhancer can be visible in such situations.

To provide a comprehensive disclosure without unduly lengthening thisspecification, applicants incorporate by reference, in their entireties,the disclosures of the above-cited patents and applications, along withU.S. patent application Ser. No. 10/027,783, filed Dec. 19, 2001(published as U.S. 2002-0126872 A1). The particular combinations ofelements and features in the above-detailed embodiments are exemplaryonly; the interchanging and substitution of these teachings with otherteachings in this application and the incorporated-by-referencepatents/applications are also contemplated.

Although not belabored herein, artisans will understand that the systemsand methods described above can be implemented using a variety ofhardware and software systems. Alternatively, dedicated hardware, orprogrammable logic circuits, can be employed for such operations.

In view of the wide variety of embodiments to which the principles andfeatures discussed above can be applied, it should be apparent that thedetailed embodiments are illustrative only and should not be taken aslimiting the scope of the invention. Rather, we claim as our inventionall such modifications as may come within the scope and spirit of thefollowing claims and equivalents thereof.

1. A method comprising: receiving digital data corresponding to aphysical document; utilizing a programmed multi-purpose electronicprocessor, transforming the digital data into a frequency domain;comparing characteristics associated with the transformed digital datato predetermined characteristics that are associated with a firstdocument category, and if the characteristics coincide, determining thatthe physical document is of the first document category; and if thecharacteristics do not coincide, comparing the characteristics of thetransformed digital data to predetermined characteristics that areassociated with a second document category, and if the characteristicscoincide, determining that the physical document is of the seconddocument category.
 2. The method of claim 1, wherein the predeterminedcharacteristics comprise a radius.
 3. The method of claim 1, wherein thepredetermined characteristics comprise a horizontal distance from a DCcomponent response to a frequency point.
 4. The method of claim 3wherein the predetermined characteristics further comprise an angleformed between a line from the origin to the frequency point and ahorizontal axis.
 5. The method of claim 1 wherein received digital datacorresponds to optical scan data.
 6. The method of claim 1 wherein thecharacteristics associated with the transformed digital data correspondto steganographic indicia hidden on or in the physical document.
 7. Aprogrammed computing device storing instructions in memory, saidinstructions are executable by said programmed computing device toperform the acts of claim
 1. 8. A computer readable media comprisinginstructions stored thereon to cause a multi-purpose electronicprocessor to perform the acts of claim
 1. 9. A computer readable mediumcomprising instructions stored thereon to cause a multi-purposeelectronic processor to perform the following acts: receive digital datacorresponding to a physical document; transform the digital data into afrequency domain; compare characteristics associated with thetransformed digital data to predetermined characteristics that areassociated with a first document category, and if the characteristicscoincide, determine that the physical document is of the first documentcategory; and if the characteristics do not coincide, compare thecharacteristics of the transformed digital data to predeterminedcharacteristics that are associated with a second document category, andif the characteristics coincide, determine that the physical document isof the second document category.
 10. The computer readable medium ofclaim 9 where the received digital data corresponds to optical scandata.
 11. The computer readable medium of claim 10 where the opticalscan data comprises visible light scanning.
 12. A computer readablemedium comprising instructions stored thereon to cause a multi-purposeelectronic processor to perform the following acts: receive digital datacorresponding to a physical document; transform the digital data into afrequency domain; compare characteristics associated with thetransformed digital data to predetermined characteristics that areassociated with a first document category, in which the predeterminedcharacteristics comprise a radius, and if the characteristics coincide,determine that the physical document is of the first document category;and if the characteristics do not coincide, compare the characteristicsof the transformed digital data to predetermined characteristics thatare associated with a second document category, and if thecharacteristics coincide, determine that the physical document is of thesecond document category.
 13. A computer readable medium comprisinginstructions stored thereon to cause a multi-purpose electronicprocessor to perform the following acts: receive digital datacorresponding to a physical document; transform the digital data into afrequency domain; compare characteristics associated with thetransformed digital data to predetermined characteristics that areassociated with a first document category, in which the predeterminedcharacteristics comprise a horizontal distance from a DC componentresponse to a frequency point, and if the characteristics coincide,determine that the physical document is of the first document category;and if the characteristics do not coincide, compare the characteristicsof the transformed digital data to predetermined characteristics thatare associated with a second document category, and if thecharacteristics coincide, determine that the physical document is of thesecond document category.
 14. A computer readable medium comprisinginstructions stored thereon to cause a multi-purpose electronicprocessor to perform the following acts: receive digital datacorresponding to a physical document; transform the digital data into afrequency domain; compare characteristics associated with thetransformed digital data to predetermined characteristics that areassociated with a first document type, in which the predeterminedcharacteristics comprise an angle formed between a line from the originto the frequency point and a horizontal axis, and if the characteristicscoincide, determine that the physical document is of the first documenttype; and if the characteristics do not coincide, compare thecharacteristics of the transformed digital data to predeterminedcharacteristics that are associated with a second document type, and ifthe characteristics coincide, determine that the physical document is ofthe second document type.
 15. A computer readable medium comprisinginstructions stored thereon to cause a multi-purpose electronicprocessor to perform the following acts: receive digital datacorresponding to a physical document; transform the digital data into afrequency domain; compare characteristics associated with thetransformed digital data to predetermined characteristics that areassociated with a first document category, in which the characteristicsassociated with the transformed digital data correspond tosteganographic indicia hidden on or in the physical document, and if thecharacteristics coincide, determine that the physical document is of thefirst document category; and if the characteristics do not coincide,compare the characteristics of the transformed digital data topredetermined characteristics that are associated with a second documentcategory, and if the characteristics coincide, determine that thephysical document is of the second document category.
 16. An apparatuscomprising: an input or interface to receive digital data correspondingto a physical document; a controller including a multi-purposeelectronic processor configured to control: i) transforming the digitaldata into a frequency domain; ii) comparing characteristics associatedwith the transformed digital data to predetermined characteristics thatare associated with a first document category, and if thecharacteristics coincide, iii) determining that the physical document isof the first document category; and iv) if the characteristics do notcoincide, comparing the characteristics of the transformed digital datato predetermined characteristics that are associated with a seconddocument category; and v) if the characteristics coincide, determiningthat the physical document is of the second document category.
 17. Theapparatus of claim 16 in which said controller is executing in a stateto perform at least one of the recited functions.